Scleroderma is a devastating connective tissue disease. An increase in dermal collagen synthesis is central to its pathogenesis. This increase has been linked to deficiency of the integrin collagen receptor alpha1beta1 in scleroderma fibroblasts, and also to an excess of dermal TGFbeta. Studies of normal fibroblasts suggest that integrin alpha1beta1 is a sensor for extracellular matrix collagen and mediates feedback inhibition on collagen synthesis. It has also been shown that TGFbeta causes upregultion of integrin alpha1beta1 in fibroblasts. We therefore propose that: 1) Increased collagen deposition in scleroderma is due to lack of normal feedback inhibition of synthesis mediated by integrin alpha1beta1, and 2) That the reduced levels of alpha1beta1 seen in scleroderma fibroblasts may be due to an aberrant response to TGFbeta. We propose studies that will enable us to determine the role of integrain alpha1beta1 in scleroderma, and which may suggest routes for pharmacologic intervention at a key step in fibrosis. We have generated mice deficient in integrin alpha1 by gene targeting. Fibroblasts derived from these animals show increased synthesis of collagen I mRNA compared to wild type. We will examine collagen turnover in these animals by complementary in vitro and in vivo approaches. We will compare collagen synthesis by alpha1beta1 deficient and wild type fibroblasts in monolayers and in 3D gels, and examine the effect on collagen synthesis of addition to these cells of alpha1 antibody, alpha1 ligands, and TGFbeta. We will examine collagen turnover in the skin of alpha1beta1 deficient and wild type animals, and determine whether the fibrotic effects of TGFbeta injection are augmented by alpha1 deficiency. We will isolate alterations in collagen synthesis from alterations in collagen breakdown in vivo by crossing alpha1 deficient mice will collagenase resistant mice. We will thus obtain a sensitive assay for the role of alpha1beta1 in regulating collagen synthesis in vivo. We will also examine genetic interactions between alpha1 deficiency and the Tight skin mouse mutation. These studies will enable us to determine the role of integrin alpha1beta1 in scleroderma, and may direct us in future to dissect the alpha1 signalling pathway as a target for anti- fibrotic agents.